This invention relates to techniques for forming a matte finish on a glass article such as an optical fiber or a glass plate.
In the manufacture of glass articles, such as plate glass, it is often desirable to reduce glare by forming a textured surface, known as a matte finish, on the article to scatter light and reduce specular reflections. The following patents are representative:
H. Niederprun et al., U.S. Pat. No. 4,055,458, discloses the mat (matte) etching of glass (e.g., plate glass) by means of liquids containing hydrofluoric acid and a soluble fluorine-containing wetting agent, e.g., perfluoroalkane sulfonic acid quaternary ammonium salt, a perfluoroalkane carboxylic acid salt, an alkoxylation product of a perfluoroalkane sulfonamide, or the like.
J. W. Falls, U.S. Pat. No. 3,616,098, describes glare-reducing glass produced by including an undissolved inorganic salt (e.g., potassium bifluoride, sodium bifluoride or calcium phosphate) in a hydrofluoric acid bath saturated with ammonium bifluoride or other salt.
On the other hand, in optical fiber technology, in particular the silica fiber segment of that art related to hermetic packaging of optoelectronic devices, it is well-known to form a metal coating on the exterior silica surface (cladding) of the fiber in order to solder the fiber to the package. The prevalent prior art technique for depositing the metal coating is sputtering. This approach, however, is not without its limitations: (1) The need for a sputtering machine is cumbersome and expensive; (2) Most sputtering machines are designed to deposit metal onto planar (e.g., semiconductor wafer) surfaces. The cylindrical surface of a fiber and pragmatic considerations have led prior art workers to utilize two separate sputtering steps-the first to deposit metal onto essentially half the cylindrical surface and the second to deposit onto the other half. However, where the "halves" meet, undesirable seams are formed which decrease reliability; and (3) The sputtering process requires a vacuum environment to reduce background contamination. This requirement inherently precludes having attached to the fiber anything which would introduce contamination into the vacuum chamber. Thus, one would remove the plastic jacket which coats the fiber and, furthermore, would avoid attaching a silicon block mount or pigtail connector, for example.
Therefore, a metal deposition process which can uniformly coat curved surfaces and which is not so contamination sensitive, such as electroplating, might be more desirable were it not for the fact that the electroplating of metal onto glass fibers suffers from poor adhesion.